Over on "thrifty tips" we've discussed the benefits of slow cookers & Remoskas.
On a larger scale - we are building our own house: as "green" as we can make it, but as always, life is not simple. For instance - do you get the most efficient insulation (with more carbon-capture in the manufacture) or stuff like sheeps' wool that is "greener" in manufacture, but less efficient?
Do you re-use grey water, which means electric pumps & double plumbing?
We looked at ground-source heat pumps 3 separate times, each time deciding that it was not worthwhile, then being persuaded by someone that we should look again. Finally - no. The Centre for Alternative Technology reckons that you should not generally use any heat-source pump with a co-efficient of less than 4, and the Energy Saving Trust reckons pumps are averaging at present less than 3 (whatever the manufacturers say). They will undoubtedly become more efficient soon, but we need to install it now.
We shall be having solar heated hot water, photo-voltaic cells, and a mechanical heat recovery unit; so the answer for the first 10 years or so is: paying off the cost of installation!